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Glucose Tolerance Test(GTT): Introduction, Procedure, Result-Interpretation, and Keynotes

Introduction of Glucose Tolerance Test

The glucose tolerance test (GTT), also known as the oral glucose tolerance test (OGTT) is useful to measure the body’s response to sugar (glucose)and it can be used to screen for type 2 diabetes. More commonly, a modified version of the glucose tolerance test is called the glucose challenge test (GCT) which is used to find gestational diabetes -a type of diabetes that develops during pregnancy.

Glucose Tolerance Test(GTT)

Test Requirements

  • 75 gm glucose
  • Glass
  • Water
  • Blood sample

Procedure of Glucose Tolerance Test

The GTT is done in several steps. After arriving at the laboratory, a phlebotomist will take a sample of blood from a vein in your arm. This blood sample will be used to measure your fasting blood glucose level. The health care provider’s office/lab will provide 75 gm sugar and a glass with water having nearly 237 ml of water that you have to drink and wait for 2 hours. Just after the completion of 2 hours, a blood sample will be taken from a vein in your arm. This blood specimen will be used to measure your blood sugar level. After the GTT, you can return to your usual activities immediately.

Result-Interpretation of GTT

GTT is tested for type 2 diabetes and two hours after drinking the glucose solution report
will be as follows-

RangeCondition
<140 mg/dL (7.8 mmol/L)Normal
140 and 199 mg/dL (7.8 and 11 mmol/L)Impaired glucose tolerance, or prediabetes
≥200 mg/dL (11.1 mmol/L)Diabetes
Table: Result-Interpretation of GTT

Keynotes on Glucose Tolerance Test

  • Prediabetic condition is also at risk of developing heart disease, even if you don’t develop diabetes.
  • GTT is a presumptive or screening test for diabetes and thus use of another blood test is mandatory to confirm the diagnosis.
  • For 8 hours before the test, a patient will not be able to eat or drink anything. He/she might want to fast overnight and schedule the test for early the following morning.
  • In a three-hour glucose tolerance test, 100 gm of glucose is given in 237 ml of water.
Medical Lab Notes

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